Runaway Wrecker

[SixSpeed]

Hey Guys,

Need to find out whats wrong with my M816. It has developed this problem slowly over the course of a few months. Basically, if you let the truck idle for a while (ie, when using the crane), when you go to accelerate again the engine will want to run away for a few seconds. At first it was only if it idled for an excessive amount of time, but now even 5 minutes idling and the engine will want to drive itself for a couple seconds. Doesn't sound healthy when it does, sounds like one cylinder is doing the running away. Makes plenty of white/grey smoke when it happens.

Engine seems to run good, it gets the heavy truck down the road alright. Only real "issue" is that it sounds a little noisy, like if the valves were out of adjustment.

I have worked on my fair share of light/medium duty diesels but I have NO experience with engines like the 250.

If anyone has any suggestions, or could get me pointed in the right direction it would be much appreciated!

 

[wreckerman893]

Having had a wrecker with the 250 Cummins in it that ran away I can tell you that it is not a pleasent experience.

If motor oil is getting into one of the cylinders from some source it could cause it to do that and put out the smoke.

In my case fuel had filled up the crankcase and that caused the runaway.

You might have a leaky seal.

Time to do some serious trouble shooting.

 

[area52]

What RPM's does the engine put out when it "runs away"? If it is just going up on the governor ( like around 2300 rpm I think), then it might be your IP or governor not working properly.

 

[goodguyzy]

I agree, white smoke=oil. that's as far as my experience level goes

 

[R Racing]

Also if the fuel lines are sucking air they can climb in RPM as well.so check your fuel system.

 

[wreckerman893]

Also if the fuel lines are sucking air they can climb in RPM as well.so check your fuel system.

The O-rings in the fuel selector switch are notorious for drying out and allowing air to be sucked into the system.

That would be my first suspect. I had that problem on my 816 and had to bypass it.

 

[papabear]

The O-rings in the fuel selector switch are notorious for drying out and allowing air to be sucked into the system.
That would be my first suspect. I had that problem on my 816 and had to bypass it.

Damaged O-rings and "runoff" situations have also been caused by "magic" fuel containing paint thinner...or so I've heard!

 

[4x4 Forever]

 

[WillWagner]

White smoke usually means an injection timing issue, i.e. air introduced into the fuel, air compresses, fuel don't. Timing can't slip on one of these, it's done with a hefty cam key and shims under the cam boxes. When an injector is removed from an 855 and another installed, at start up it had a pretty good fuel knock and lets out a good size cloud of grey smoke, that smoke isn't a timing issue, just a case of waayy too much fuel in the cylinder that isn't atomized. You might have a split cup on an injector. That would give the engine a funny sound like maybe a marble in one cylinder, the heavy whitish grey smoke and the RPM hanging up after idle. Split cups happen from incorrect adjustment, fuel tanks higher than the cylinder heads or restricted return lines. Try running the engine out of and into a bucket of fuel and see if it runs the same, that will eliminate the fuel lines and let you know if you need to check the chassis or if it is an engine issue.

Also, these engines have little holes in the heads, under the rocker boxes that run into the intake. If you have too much oil in the engine or there is an issue of the oil not getting off the head fast enough, like a broken rocker shaft, it will suck the oil into the hole and the engine will uncontrollably run away. very uncommon, but I have seen it. Since your engine runs OK going down the raod though, I don't think this an issue.

 

[augiedoggy]

Sixspeed, like the others said, maybe your oil level is too high and oil is being sucked out of the crankcase, effectively giving it more fuel.??
After reading wreckermans horror story of his runaway, i keep the air cleaner mushroom cover loose and a board by the drivers seat to block off the air......just in case!!
Also, when offroading my 818 and creeping down a steep hill mine will tend to start accelerating on its own, then i blip the throttle and behaves again, not sure what thats about, throttle linkage?

previously my 818 was smoking bad, running rough and got lots of fuel in the oil due to misadjusted injectors.
http://www.steelsoldiers.com/5-ton-up/73256-nhc250-valve-injector-overhead-adjusting.html

good luck!

 

[Scrounger]

I would start with the basics and check the fuel filter/ water separator. If there is any water in the filter the engine will do some of the things that have going on, ask me how I know. The injector pump requires fuel to run properly and if the filter doesn’t allow fuel to flow the engine will become fuel starved and do some strange things.

 

[Floridianson]

One thing about the 250 without skirt oilers is don't let them idle to long. When useing the hyd's on the rear you use the rear throttel control and the second gov. comes into play and holdes it at 1500 rpm.

 

[73m819]

on the 819, run at about 1200 in 4th (-10 says 1250 in 4th)

 

[vinny-socom1]

sounds like user error...

Vinny

 

[Floridianson]

Yea that was a close guess on my part but somewhere around there on the rpm.
When you say runaway do you mean you hit the throttel and continues to rize after you let off then comes back
down? Did I say DON'T idle these motors!!!!!!!!!!!!!

 

[sandcobra164]

Cylinder's are loading up on fuel. Here's an experiment to try. Partially block off the air supply at idle until it's idling very low, say 300 rpm, due to the lack of air. Wait about 10 seconds or so till you start to see some black smoke and then remove the restriction. It'll rev up with no help from you. A Multi is great for this test as it actually burns pretty clean at idle and has a pretty awesome combustion chamber. The reason your motor tries to run away is at idle, the cylinders are partially loading up on raw fuel drops, when you go to rev it up, those droplets atomize once the pistons start moving faster, and then it turns into burnable fuel again. Motor raises cain till it get's rid of it. It's not quite a runaway as the gov. on the PT pump will stop all fuel going to the injectors once it's reached and there shouldn't be that much fuel in the cylinders to burn off but you could very well wind up with an expensive hole being formed on the side of the block, I just hope not. Could be an injector issue but like Floridianson said, don't let it idle for long periods, run it up to about 1500 when using the crane. This will ensure complete combustion of the fuel.

 

[USAFSS-ColdWarrior]

RUNAWAY WRECKER ! ? ! ?

Try putting it's picture on the bulletin board in the entryway of your local WalMart AND on Milk Cartons. They do that for runaway kids and it seems to help sometimes.....

OK - I know that was some crass humor. SORRY.

On a serious note: Good luck with your trouble-shooting and corrective efforts.

 

[spicergear]

on the 819, run at about 1200 in 4th

On my deuce with the crane, I run 4th gear at about 1200rpm too. Spins the transfercase PTO fast enough to run the crane at speed and enough power to overcome the load holder valves on the main lift rams. Booming down will still drop the engine rpm a little at 1200, but it will drop a lot more if I'm at lower rpm or sometimes not build the pressure to overcome the load holders if the rpm is down. Run her up a little and all it well.

Over the past few years diesel people have started saying that idling for long periods of time isn't that good for the engine anyway as the cooler combustion leaves more deposits in the combustion chamber.

I think sandcobra is onto something. Especially considering how long most of these things have sat around. I'd bet 4 out of 6 injectors out of darn near anyone's engine doesn't have the perfect spray pattern to it.